I used MyUnity to try some themes such as clearlooks and industrial and then I switched back to default. Now my Launcher is broken. How can I repair this?

There are many invisible items in the Launcher, such as shown here above the Google Chrome icon.

Edit:unity --reset results in thousands of error messages and warnings and the complete loss of the Launcher and top-of-screen task-strip. The execution of this command might take 15 minutes or more. unity --reset-icons also executes for at least 15 minutes, spews errors, and does not resolve the problem.